1. Field of the Invention
The present invention relates to a toner carrier used in an image forming device such as copier, facsimile machine, or printer, in particular, to a toner roller provided as a toner roller in a process cartridge or a develop unit of the image forming device.
2. Description of the Related Art
Heretofore, various types of develop unit have been used in an image forming device to develop an electrostatic latent image formed on an image carrier. Two kinds of develop unit, a two-component develop unit using a developer containing tonner and carrier and a one-component develop unit using only toner as a developer are well known.
There are two types of one-component develop unit, that is, contact type and non-contact type. A contact-type develop unit develops an electrostatic latent image on the surface of an image carrier by allowing the toner on a toner carrier to contact the surface of the image carrier. Meanwhile, in a non-contact type develop unit the toner carrier is disposed to oppose the image carrier with a certain interval. It is configured to apply an alternating voltage to the toner carrier and generate an alternating electric field between the toner carrier and the image carrier to supply the toner from the toner carrier onto the image carrier and develop an electrostatic latent image thereon.
The toner carrier includes a metal core and a barrel on the outer circumference of the metal core. The barrel generally includes an elastic layer made from solid rubber or porous material as sponge.
Such a develop unit for use in the image forming device has a problem in leakage of toner from a gap between both ends of the barrel and a developer container. In particular a toner leakage is most likely to occur in the periphery of both ends of the barrel since it corresponds to an opening of the developer container.
Magnetic shielding effect does not apply to the one-component develop unit not containing carrier since toner is non-magnetic. To prevent the toner from leaking from the periphery of the barrel of the tonner carrier, it is needed to occlude the space without a gap between both ends of the barrel and the opening of the developer container by pressing other elements onto a develop roller.
An end seal element can be provided to seal both ends of the barrel and block the toner from leaking outside. A restriction element such as a blade roller is used to properly limit the amount of toner and avoid an excessive toner from protruding. Japanese Patent Application Publication No. 2005-309191 (Reference 1), for example, discloses an auxiliary seal with which the gap between the restricting element and the end seal element is hermitically closed.
However, since the barrel of the toner carrier rotates with its both ends pressed onto the end sealer, a toner leakage may still occur over a long-term use due to wear-out of both ends by friction. Further, because of a friction heat occurring between both ends and the seal element, the temperature inside the developer container rises, deteriorating the toner. This results in toner's adhering on the restriction element, causing the generation of an image with white streaks and a toner dispersion which contaminates the inside of the image forming device.
In view of these problems, Japanese Patent No. 4561780 (Reference 2) discloses blasting the outer circumferences of both ends of the barrel and reducing a surface roughness of a blasted area.
Further, Japanese Patent No. 4404108 (Reference 3) discloses forming a spiral-form area on the outer circumferences of both ends of the barrel and setting the angle between the direction of the spiral and the rotational direction of the toner carrier to a sharp angle to prevent toner from leaking outside.
Moreover, Japanese Patent No. 3952428 (Reference 4) discloses providing a conductive layer on the outer circumference of a metal core and a coating containing polymethylsilsesquioxane on both ends of the outermost conducive layer, thereby to prevent a toner leakage due to a chipping or abrasion of barrel ends.
Meanwhile, along with high-speed operation of the image forming device, toner is more likely to enter between the barrel ends and end seal element, which may cause a toner dispersion or a frictional heat caused by the contingence between the toner and the barrel ends.
For example, References 2 and 3 use a hard roller having no elastic layer. Because of its hardness, the hard roller's adhesion with the end seal element is low, likely causing a toner leakage. To prevent the toner leakage, the pressing force of the barrel ends relative to the end seal element needs to be enlarged, leading to the generation of a frictional heat. Especially, the barrel is not made from a material with a low friction coefficient, therefore, it likely causes a frictional heat.
In Reference 4 there is no difference in the lengths of the outer circumference and inner circumference of the coating. Because of this, it cannot sufficiently seal toner over a long-time use or in high-speed operation of the image forming device, so that the toner may leak from both ends of the toner roller.